Process for producing polyarylene sulfide

ABSTRACT

A process for producing polyarylene sulfide includes: steps of reacting an aromatic dihalide compound and an alkaline metal compound in a polar organic solvent for polymerization under heating and cooling a system including the reaction mixture to recover particulate polyarylene sulfide (PAS). The system after the reaction is gradually cooled at an average cooling speed of 0.2 to 1.0 deg. C./min. selectively in a temperature range of from 1 deg. C. below to 1 deg. C. above a maximum system-viscosity temperature. As a result, the process can be operated at a relatively short polymerization cycle and yet provides the product PAS particles with a high and stable bulk density as to exhibit good processability in the transportation and storage, and excellent transportability in a hopper or a screw of an extruder or a molding machine.

TECHNICAL FIELD

The present invention relates to a process for producing a polyarylenesulfide (hereinafter sometimes abbreviated as “PAS”), more particularlyto a process for effectively producing high-quality PAS.

BACKGROUND ART

PAS as represented by polyphenylene sulfide (hereinafter sometimesabbreviated as “PPS”) is an engineering plastic which is excellent inproperties, such as heat resistance, chemical resistance, flameretardancy, mechanical strength, electrical properties, and sizestability. PAS can be formed into various shaped products, film, sheet,fiber, etc., by ordinary melt-forming processes, such as extrusion,injection molding, and compression molding, and is therefore widely usedin versatile fields, inclusive of electrical and electronic industriesand car industries. Further, powdery PAS may also be used in the fieldsof, e.g., coatings on metals and other materials.

A typical process for producing PAS may comprise a step of reacting anaromatic dihalide compound and an alkaline metal compound in a polarorganic solvent such as an organic amide under heating forpolymerization (and condensation) (hereinafter referred to as a“reaction step” or “polymerization step”), and steps disposed before andafter the reaction step. Principal steps disposed after the reactionstep may include: a step of cooling the reaction mixture including theproduced PAS to or below a temperature at which the reaction mixtureexhibits a vapor pressure below the atmospheric pressure (hereinafterreferred to as a “cooling step”) and a step of isolating PAS from thecooled mixture including PAS (hereinafter referred to as a“washing-filtration-drying step”).

In some cases, a dehydration step for adjusting moisture in the systemis placed prior to the (polymerization) reaction step that is performedby adding the aromatic dihalide compound. More specifically, in thiscase, PAS is produced through a combination of respective stepsincluding the dehydration step, the polymerization step, the coolingstep, the washing-filtration-drying step, a step of recovering unreactedstarting materials, and a step of recovering the polar organic solvent.

Regarding the cooing step, Japanese Laid-Open Patent Application (JP-A)59-49232 discloses a process for producing polyarylene sulfide whereinthe system after the polymerization is gradually cooled at a rate slowerthan 50° C./min. from the polymerization temperature down to atemperature of 240° C. or below, thereby precipitating the polymerparticles and providing fine polymer crystals having sizes of at least60 Å. The JP reference however includes various descriptions regardingthe gradual cooling temperature and the gradual cooling rate, such asdown to 240° C. or below, preferably down to at least 200° C. or belowfor the gradual cooling temperature region, and a rate slower than 50°C./min., preferably a rate slower than 10° C./min. for the gradualcooling rate. Particularly, in the working examples, there are discloseda mode of gradual cooling at a rate of 1° C./min. from 260° C. down to150° C. (Example 1) and a mode of gradual cooling at a rate of 0.5°C./min. from 260° C. down to 100° C. (Example 2). Accordingly, theseExamples require cooling periods of 110 min. and 220 min. respectivelyfor the cooling from 260° C. down to 150° C.

JP-A 2001-89569 discloses a process for producing PAS particles of highpurity through a short polymerization process time by controlling thecooling rate within a range of 0.2-1.3° C./min. in a temperature rangeof 245° C. or below, based on a knowledge that the formation of polymerparticles and the amount of by-products in the resultant polymerparticles are affected by the mol ratio of the aromatic polyhalidecompound to the polar organic solvent and the cooling rate after thepolymerization reaction. The JP reference describes only the reductionin amount of the resultant by-products generated as gases when theproduct PAS is heated, as the effect of the gradual cooling, and doesnot refer at all to any other properties of PAS. Further, as for thecooling temperature range, Example 1 refers to 245° C. to 218° C.;Example 2, 245° C. to 212° C.; and Example 3, 245° C. to 210° C. Thismeans that if the temperature range of 245° C. to 218° C. is subjectedto gradual cooling at the upper limit cooling rate of 1.3° C./min., thegradual cooling requires a period of at least 20 min., and theshortening of the polymerization cycle including the cooling step is notyet at a satisfactory level.

DISCLOSURE OF INVENTION

In view of the above-mentioned circumstances of the prior art, aprincipal object of the present invention is to provide a process forproducing through a relatively short polymerization cycle time such PASparticles having a high and stable bulk density as to exhibit goodprocessability in transportation and storage, and excellenttransportability in a hopper or a screw of an extruder or a moldingmachine.

A further object of the present invention is to apply theabove-mentioned process to a PAS production process including aphase-separation polymerization system capable of producinghigh-molecular weight PAS particles.

As a result of our study with the above-mentioned objects, we havediscovered that an extremely limited temperature region in the course ofcooling after the polymerization under heating, that is a temperatureregion of maximum system-viscosity temperature ±1° C. selectively andessentially determines the particle properties as represented by bulkdensity of product PAS particles. Herein, the maximum system-viscositytemperature refers to a temperature at which a reaction system (i.e.,the content in the reaction vessel) assumes a maximum viscosity in thecourse of the cooling. More specifically, it is known that in a reactionvessel after the completion of polymerization involving thephase-separation polymerization system capable of producinghigh-molecular weight PAS, PAS is present in a molten state and isphase-separated into a thick phase and a dilute phase. Then, if thesystem is cooled under stirring, PAS is solidified from the molten stateand is caused to be present as a powdery, particulate or granular solidin a suspended state. During this stage, the change in system-viscosityoccurs. More specifically, when the dispersion system including themolten PAS is cooled under stirring, the apparent viscosity of theentire system gradually increases due to the viscosity increase of PAScaused by the cooling, and below a certain temperature (i.e., themaximum system-viscosity temperature), the apparent viscosity of theentire system becomes lower. The maximum system-viscosity temperaturecan be detected by observation of a stirring torque or a power supply tothe stirrer under a constant stirring speed. Further, according to ourstudy, it has been found that the cooling speed in the extremely limitedtemperature region of the maximum system-viscosity temperature ±1° C.determines the particle properties as represented by the bulk density ofthe product PAS particles (that is, a lower cooling speed within therange of 0.2-1.0° C./min. tends to result in a higher bulk density ofthe product PAS particles) and the cooling speed at temperatures outsidethe temperature region does not essentially influence the particleproperties of the product PAS particles. Accordingly, it becomespossible to produce PAS particles having good particle properties whileshortening the entire polymerization cycle through shortening of theentire cooling time, if the system is subjected to gradual coolingwithin the above-mentioned temperature range of the maximumsystem-viscosity temperature ±1.0° C., and in temperature ranges outsidethe temperature range, the system is subjected to cooling at as large acooling speed as possible, preferably by adopting a cooling meansallowing rapid cooling.

Thus, according to the present invention, there is provided a processfor producing polyarylene sulfide, comprising: reacting an aromaticdihalide compound and an alkaline metal compound in a polar organicsolvent for polymerization under heating, and cooling a system includingthe reaction mixture to recover particulate polyarylene sulfide, whereinthe system after the reaction is gradually cooled at an average coolingspeed of 0.2 to 1.0° C./min. selectively in a temperature range ofmaximum system-viscosity temperature ±1° C.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinbelow, the present invention will be described more specificallywith respect to preferred embodiments.

(Alkaline Metal Compound)

Examples of the alkaline metal compound used in the present inventionmay include: alkaline metal sulfides, such as lithium sulfide, sodiumsulfide, potassium sulfide, rubidium sulfide, cesium sulfide, andmixtures of two or more species of the above. These alkaline metalsulfides are generally sold in the form of hydrates and may be used assuch. Examples of the hydrates may include: sodium sulfide nona-hydrate(Na₂S.9H₂O) and sodium sulfide penta-hydrate (Na₂S.5H₂O). The alkalinemetal sulfide may also be used as an aqueous mixture. Further, thealkaline metal sulfide can also be prepared in situ in an organic amidesolvent from alkaline metal hydrosulfide and alkaline metal hydroxide.It is also possible to use an alkaline metal hydroxide together with analkaline metal sulfide so as to have the alkaline metal hydroxide reactwith a minor amount of alkaline metal hydrosulfide or alkaline metalthiosulfate possibly contained in the alkaline metal sulfide, therebyremoving or converting the minor amount component into alkaline metalsulfide. Among the alkaline metal sulfides, sodium sulfide and sodiumhydrosulfide are particularly preferred in view of the inexpensiveness.

Water to be removed in the dehydration step in the production process ofthe present invention may include: hydrate water of the above-mentionedhydrate, aqueous medium of the aqueous mixture, water by-produced by thereaction between the alkaline metal hydrosulfide and the alkaline metalhydroxide, etc.

(Aromatic Dihalide Compound)

The aromatic dihalide compound used in the present invention is anaromatic compound having two halogen atoms directly bonded to thearomatic ring. Specific examples of the aromatic dihalide compound mayinclude: o-dihalobenzene, m-dihalobenzene, p-dihalobenzene,dihalotoluene, dihalonaphthalene, methoxy-dihalobenzene, dihalotoluene,dihalonaphthalene, methoxy-dihalobenzene, dihalobiphenyl, dihalobenzoicacid, dihalodiphenyl ether, dihalodiphenylsulfone, dihalodiphenylsulfoxide, and dihalodiphenyl ketone. Herein, the halogen atoms eachrefer to an atom of fluorine, chlorine, bromine or iodine, and the twohalogen atoms contained in one aromatic dihalide compound may be thesame or different. The aromatic dihalide compound can have one or moreof substituents, such as carboxyl group, hydroxy group, nitro group,amino group and sulfonic acid group. In the case of having pluralsubstituent groups, the species of the substituent groups may be singleor a combination of different species. These aromatic dihalide compoundsmay respectively be used singly or in combination of two or more speciesin an amount of 0.9 to 1.20 mols with respect to 1 mol of the chargedalkaline metal sulfide.

(Molecular Weight-Adjusting Agent, Branching or Crosslinking Agent)

A monohalide compound (which can be a non-aromatic compound, if desired)can be used in addition to the aromatic dihalide compound so as to forma terminal of the product PAS, regulate the polymerization reaction oradjust the molecular weight of the product PAS. It is also possible toco-use a polyhalide compound (which can be a non-aromatic compound, ifdesired) having three or more halogen atoms, an activehydrogen-containing aromatic halide compound, a halogenated aromaticnitro compound, etc. so as to form a branched or crosslinked polymer. Apreferred example of the polyhalide compound as a branching orcrosslinking agent may be trihalobenzen.

(Polar Organic Solvent)

In the present invention, it is preferred to use an organic amidesolvent that is a non-protonic polar organic solvent as a solvent forthe polymerization reaction and the product PAS recovery. The organicamide solvent may preferably be one which is stable against the alkaliat high temperatures. Specific examples of the organic amide solvent mayinclude: amide compounds, such as N,N-dimethylformamide, andN,N-dimethyl-acetamide; N-alkylpyrrolidone compounds orN-cycloalkylpyrrolidone compounds, such as N-methyl-ε-caprolactam,N-methyl-2-pyrrolidone (hereinafter sometimes referred to as “NMP”) andN-cylohexyl-2-pyrrolidone; N,N-dialkyl imidazolidinone compounds, suchas 1,3-dialkyl-2-imidazolidinone; tetraalkylurea compounds, such astetramethylurea; and hexaalkylphosphoric acid triamide compounds, suchas hexamethylphosphoric acid triamide. These organic amide solvents mayrespectively be used singly or in combination of two or more species.Among these organic amide compounds, N-alkylpyrrolidone compounds,N-chcloalkylpyrrolidone compunds and N,N-dialkylimidazolidinonecompounds are preferred, and NMP, N-methyl-ε-caprolactam and1,3-dialkyl-2-imidazolidinone are particularly preferred. The organicamide solvent used in the polymerization reaction may ordinarily be usedin an amount in the range of 0.1 to 10 kg per mol of the alkaline metalsulfide compound.

(Phase Separation Agent)

In the present invention, it is preferred to use a phase separationagent for provide two phases, i.e., a thick polymer phase and a dilutepolymer phase, in order to accelerate the polymerization to obtain ahigh polymerization-degree PAS in a short time. Specific examples of thephase separation agent may include: organic sulfonic acid metal salts,lithium halides, organic carboxylic acid metal salts, phosphoric acidalkaline metal salts and water, which are generally known aspolymerization aids for PAS. These phase separation agents may be usedsingly or in combination of two or more species. The amount of the phaseseparation agent may vary depending on the chemical species thereof butmay ordinarily be selected from the range of 0.01 to 10 mols per mol ofthe charged alkaline metal sulfide. The phase separation agent may beco-present from the stage of charging the other polymerization startingmaterials or may be added in the course of polymerization so as toprovide an amount sufficient to cause the phase separation.

(Reaction Under Heating)

In the present invention, PAS may be produced by subjecting an alkalinemetal sulfide and an aromatic dihalide compound to polymerizationreaction under heating in an organic amide solvent. The step of reactionunder heating may be divided into a dehydration step and apolymerization step. More specifically, prior to the polymerizationstep, a mixture composing an organic amide solvent and an alkaline metalsulfide and containing water is subjected to dehydration under heatingso as to adjust the water content in the polymerization system.(Dehydration step) After the dehydration step, the mixture obtained inthe dehydration step and an aromatic dihalide compound are mixed, andthe alkaline metal sulfide and the aromatic dihalide compound are heatedfor polymerization reaction in the organic amide solvent.

(Polymerization Step)

(Dehydration Step)

The dehydration step is effected by heating an alkaline metal sulfide inan organic amide solvent, desirably under an inert gas atmosphere, todistill off water out of the reaction system. The alkaline metal sulfideis ordinarily served in the form of a hydrate or an aqueous mixture andtherefore contains water in an amount larger than necessity. Further, inthe case of using an alkaline metal hydrosulfide as the sulfide source,a nearly equal mol of an alkaline metal hydroxide is added thereto, andthe two alkaline metal compounds are reacted in situ in the organicamide solvent to be converted into an alkaline metal sulfide. Water isby-produced in the conversion step. In the dehydration step, an amountof water including such hydrate water (crystalline water), aqueousmedium and by-produced water is dehydrated so as to be reduced to anecessary level. More specifically, the dehydration step is ordinarilyoperated until the water content co-present in the polymerization systemis reduced to about 0.3 to 5 mols per mol of the alkaline metal sulfide.In case where the water content is excessively reduced in thedehydration step, water may be added prior to the polymerization step soas to provide the desirable water content level.

The charging of the above-mentioned starting materials may be performedordinarily in a temperature range of room temperature to 300° C.preferably a range of room temperature to 200° C. The starting materialsmay be charged into the reaction vessel in an arbitrary order and therespective materials may be additionally charged in the course of thedehydration operation. As mentioned above, an organic amide solvent isused as the solvent for the dehydration step, and the solvent maypreferably be of the same species as the organic amide solvent used inthe polymerization step, particularly preferably NMP. The solvent mayordinarily be used in an amount of 0.1 to 10 kg per mol of the chargedalkaline metal sulfide.

The dehydration operation may be achieved by heating the composition ofmaterials charged in an temperature range of ordinarily at most 300° C.preferably 60° C. to 280° C., for a period of ordinarily 15 minutes to24 hours, preferably 30 minutes to 10 hours. The heating may beperformed at a constant temperature, at temperatures elevated stepwiseor continuously or by a combination of these. The dehydration operationmay be performed batch-wise, continuously or by a combination of these.The dehydration may be operated in an apparatus which may be identicalto or different from a reaction vessel used in the subsequentpolymerization step. In the dehydration step, a portion of the organicamide solvent is distilled off together with water by distillation, andthe water may be separated from the organic amide solvent by subsequentdistillation. Further, hydrogen sulfide is discharged together withwater or the organic amide solvent. The hydrogen sulfide discharged canbe recovered for re-utilization by an appropriate method, such asabsorption with an aqueous alkaline solution.

(Polymerization Step)

The polymerization step is performed by mixing the composition aftercompletion of the dehydration step with an aromatic dihalide compound,and heating the resultant mixture. At the time of preparing the mixture,it is possible to adjust the amounts of the organic amide solvent andwater present together therewith, and also possible to add othermaterials, such as a polymerization aid. The mixing of the compositionafter the dehydration step and the aromatic dihalide compound may beperformed in a temperature range of ordinarily 100 to 350° C. preferably120 to 350° C. The order of the mixing is not particularly restricted,and the two components may be added portion by portion or added all atonce. Further, the mixing of the hydrogen sulfide-absorbing liquid forrecovering the hydrogen sulfide discharged in the dehydration step mayalso be performed in an appropriate order.

The polymerization reaction may be performed in a temperature range ofgenerally 100 to 350° C. preferably 150 to 330° C. The heating for thereaction may be performed at a constant temperature, at temperaturesincreased stepwise or continuously, or by a combination of these. Thepolymerization reaction time is selected from a range of generally 10minutes to 72 hours, preferably 30 minutes to 48 hours. The organicamide solvent used in the polymerization step is ordinarily 0.1 to 10kg, preferably 0.15 to 1 kg, per mol of the sulfur used in thepolymerization step. The amount of the solvent can be changed during thepolymerization within the above-mentioned range.

In the present invention, it is preferred to adopt a phase-separationpolymerization mode capable of providing a relatively high-molecularweight PAS wherein a phase separation agent is added to thepolymerization system at an arbitrary time from the commencement to thecompletion of the polymerization. As the phase separation agent, it ispreferred to use water in view of the cost, easiness of removal from thepolymer, etc. In the case of causing phase separation by increasing theamount of water co-present in the polymerization system, water may beadded at an arbitrary time from the start to the end of thepolymerization. As an example of polymerization process involving awater content increased in the course of polymerization, there has beenknown a process wherein the reaction is caused to proceed in thepresence of water in an amount of 0.5 to 2.4 mols per mol of thealkaline metal sulfide up to a conversion of 50 to 98 mol % of thearomatic dihalide compound, then water is added so as to provide a watercontent of 2.5 to 7.0 mols per mol of the alkaline metal sulfide and thetemperature is elevated to 245 to 290° C. to continue the reaction(Japanese Patent Publication (JP-B) 63-33775), and the process isparticularly preferably used in the present invention.

(Cooling)

Then, the reaction system (i.e., the content in the polymerizationreaction vessel) is cooled under stirring. The cooling may be effectedaccording to a so-called indirect heat-transfer scheme of causingheat-exchange with a heat medium via a heat transfer surface and usingcooling means, such as a reaction vessel side-wall jacket contacting theliquid phase of the reaction mixture, heat-transfer tubes disposed inthe liquid phase, a side-wall jacket and heat-transfer tubes disposed tocontact the gaseous phase in the reaction vessel, and a heat-exchangeraccompanied with condensation by using, e.g., a reflux condenser. Thesecooling means may be used singly or in combination, as desired.

However, it has been discovered by us that gradual cooling should beeffected selectively in a range of extreme proximity to the maximumsystem-viscosity temperature in the course of cooling for the purpose ofimproving the properties of the product PAS particles. Accordingly, itis preferred to realize as large a cooling speed as possible intemperature regions outside the above-mentioned range, therebyshortening the entire cooling time, and therefore the entirepolymerization cycle time for achieving a good production efficiency.For this purpose, it is preferred to effect efficient cooling byadopting, among the above-mentioned cooling means, a rapid cooling meansof a better cooling efficiency, i.e., a reflux condenser disposed at anupper part of the reaction vessel (in a sense of including a coolingcoil exposed to the gaseous phase in the reaction vessel) for condensingcondensable components including water in the gaseous phase and mixingthe condensed liquid with the polymerization liquid phase understirring. In this instance, it is preferred to improve the condensationheat-transfer efficiency of the reflux condenser by removing at least aportion of non-condensable gaseous components from the gaseous phase atthe top of the reflux condenser (as disclosed in Japanese PatentApplication 2001-296545). The removal of the non-condensable gaseouscomponents from the gaseous phase may be effected by, e.g., purging outof the system.

After the polymerization reaction, the system is cooled at as large acooling speed as possible down to proximity of the maximumsystem-viscosity temperature, then gradually cooled selectively in thetemperature region of the maximum system-viscosity temperature ±1° C.,and then cooled again at an increased cooling speed down to atemperature at which the reaction mixture exhibits a vapor pressurebelow the atmospheric pressure. The maximum system-viscosity temperaturecan be easily detected as a temperature giving a maximum of power orcurrent supplied to the stirrer or a reading of a torque meter attachedto the stirring shaft.

The above-mentioned operation cycle is an ideal one based on ourdiscovery for obtaining product PAS particles having good particleproperties as represented by a high bulk density through as short acooling cycle as possible. In an actual polymerization reaction system,however, it is impossible to ignore a thermal inertia including the heatcapacity of the reaction vessel. Accordingly, in an actual coolingoperation, it is preferred to effect a preliminary test for an objectivepolymerization reaction system for obtaining system parameters inclusiveof the maximum system-viscosity temperature and a temperature cycle forrealizing the selective gradual cooling in proximity to the maximumsystem-viscosity temperature, thereby setting a realizable coolingtemperature cycle model, and to effect the control operation inclusiveof the start, stop and exchange of the cooling means, and the increaseor decrease of cooling medium supply rate, according to the coolingtemperature cycle model.

More specifically, in the process of the present invention, the systemis gradually cooled at an average cooling speed of 0.2 to 1.0° C./min.selectively in a temperature range of maximum system-viscositytemperature ±1° C. in the course of the cooling of the system. In viewof the thermal inertia of the system, however, it is practicallyimpossible to satisfy the above-mentioned condition and also realize acooling speed exceeding 1.0° C./min. over the whole regions outside therange of the maximum system-viscosity temperature ±1° C. including thevicinity of the range: Accordingly, the condition of “the system afterthe reaction is gradually cooled at an average cooling speed of 0.2 to1.0° C./min. selectively in a temperature range of maximumsystem-viscosity temperature ±1° C.” of the present invention means thatthe system is cooled at a cooling speed (not an average cooling speed)exceeding 1.0° C./min., preferably at least 2.0° C./min., furtherpreferably at least 3.0° C./min., in the temperature regions outside arange of maximum system-viscosity temperature ±3° C., preferably outsidea range of maximum system-viscosity temperature ±2° C. For the purposeof stably improving the particle properties of the product PAS particleswithout incurring a substantial increase of the cooling cycletime, it isalso preferred to keep an average cooling speed in the range of 0.2 to1.0° C./min. over a temperature range of the maximum system-viscositytemperature ±2.0° C. Incidentally, a gradual cooling speed of below 0.2°C./min. in the selected temperature range in proximity to the maximumsystem-viscosity temperature incurs an increased cooling time in thetemperature range which cannot be ignored and is thus not preferable.

(Post-Treatment)

The slurry containing the product PAS particles obtained through theabove-mentioned cooling step may be post-treated in an ordinary manner.For example, the cooled product slurry may be subjected to filtration asit is or after dilution with water, etc., and the recovered PASparticles may be subjected to a repetition of washing with water andfiltration, followed by drying, to obtain a product PAS. After theabove-mentioned filtration or sieving, PAS can be washed with an organicsolvent such as an organic amide solvent identical to the polymerizationsolvent, a ketone or an alcohol, or high-temperature water. It is alsopossible to treat the product PAS with an acid or a salt, such asammonium chloride.

(Product Polymer)

The product PAS obtained through the process of the present inventionmay be formed into various injection-molded products, and extrusionproducts, such as sheets, films, fibers and pipes, by itself or togetherwith various inorganic fillers, fibrous fillers or various syntheticresins mixed therewith.

EXAMPLES

Hereinbelow, the present invention will be described more specificallybased on Examples and Comparative Examples. It should be understoodhowever that the present invention is not restricted to such Examples.Incidentally, physical properties described herein are based on valuesmeasured according to the following methods.

(1) Polymer melt viscosity was measured at 310° C. and a shearing speedof 1200/sec.

(2) Each product after the polymerization reaction was subjected tosieving through a screen having an opening diameter of 150 μm (100 mesh)to recover a particulate polymer thereon. The yield of the particulatepolymer was calculated as a weight percentage thereof with respect to aweight (theoretical) of PAS calculated on an assumption that sodiumsulfide present in an autoclave (reaction vessel) after the dehydrationstep was fully converted into PAS.

(3) Bulk density of a polymer was measured by using a bulk specificgravity meter (made by Tokyo Kuramochi Kagaku Kiki Seisakusho K.K.)according to JIS-K6721.

(4) A maximum system-viscosity temperature was detected based on amaximum value of consumed power measured by a clamp power meter(“CW140”, made by Yokogawa Denki K.K.) disposed on a stirrer motor forthe autoclave.

Example 1

Polymerization and cooling were performed by an apparatus including a 20liter-autoclave (reaction vessel), and a cylindrical condenser having aninner diameter of 40 mm and a height of 250 mm and vertically installedat the top of the autoclave. The autoclave was further equipped with anelectric heater capable of heat conduction from the side wall surface, athermometer and a pressure gauge for detecting the inner temperature andpressure, and a stirrer. The condenser was equipped with a thermometerfor measuring a temperature of the upper gaseous phase.

More specifically, 6,000 g of NMP and 3500 g of sodium sulfidepenta-hydrate containing 45.9 wt. % of sodium sulfide (Na₂S) werecharged in the reaction vessel, and after aeration with nitrogen gas,the system was gradually heated to 200° C. under stirring, therebydistilling off 1449 g of water and 1015 g of NMP. In this instance, 0.43mol of H₂S was discharged by vaporization. Accordingly, the effectiveamount of Na₂S in the reaction vessel after the dehydration step wasreduced to 20.14 mols. The vaporized H₂S corresponded to 2.10 mol. % ofthe charged Na₂S.

Then, the reaction vessel containing 20.14 mols of effective Na₂S wascooled to 180° C., and 3004 g of p-dichlorobenzene(pDCB)[pDCB/Na₂S=1.015 (by mol)], 3073 g of NMP, 114 g of water (totalwater content/Na₂S=1.50 (by mol)] and 35 g of NaOH (purity: 97%) so asto provide 6.00 mol % of NaOH with respect to the effective Na₂S in thevessel were further charged to the vessel. Incidentally, the vesselalready contained 0.86 mol of NaOH produced by the vaporization of H₂S.

The system was heated at 220° C. to cause reaction for 4.5 hours underoperation of the stirrer at 250 rpm, then 472 g of water as the phaseseparation agent (giving a mol ratio of total water/Na₂S=2.8 in thevessel) was injected under pressure, and the system was heated to 260°C. for 5.0 hours of reaction to complete the polymerization.

After completion of the polymerization, the system was cooled in amanner described below. (Incidentally, the apparatus used in thisExample was of a relatively small size, so that the cooling speed wascontrolled by controlling the operation conditions of theabove-mentioned heater and condenser in combination with air-fan coolingfrom outside the polymerization vessel. In a larger-scale apparatus,however, the air-fan cooling (and heater) will be replaced by indirectheat exchange by a side-wall jacket or an intra-vessel cooling coilsupplied with a thermal medium for controlling the cooling speed.)

More specifically, after completion of the polymerization, power supplyto the side-wall heater was cut off at a temperature of 260° C. insidethe vessel and cooling water was supplied to the condenser to start thecooling. Thereafter, the water supply rate to the condenser and the airsupply rate to the outer wall of the polymerization vessel werecontrolled and a valve at the top of the condenser was opened asrequired for purging non-condensable gas out of the polymerizationvessel, thereby effecting the cooling according to a temperature profileshown in Table 1. In the course of cooling, at a time of 7.5 minutesfrom the start of the cooling, a maximum of stirring power (162 W) wasdetected at a temperature of 229.7° C. (inside the vessel) to confirmthe maximum system viscosity, and the temperature reached 228.7° C.after 2 minutes thereafter. Table 1 shows temperatures corresponding tothe maximum system-viscosity temperature +5° C., +3° C., +2° C., +1° C.,±0° C. (maximum system-viscosity temperature), −1° C., −2° C., −3° C.,and −5° C., time after the start of cooling at the respectivetemperatures, an average cooling speed in the temperature range ofmaximum system-viscosity temperature ±1° C., and average cooling speedsin temperature regions outside the temperature range.

A time period from the start of the cooling to 150° C. was 31 minutes.Thereafter, the reaction liquid was taken out of the reaction vessel.

(Washing-Drying)

The thus-obtained reaction mixture was subjected to 3 cycles ofwashing-filtration by adding acetone, followed by 4 times of washing byadding room-temperature water. The resultant slurry was subjected towashing with acetic acid aqueous solution added thereto and filtration,followed further by four times of washing with water and sieving torecover a solid wet resin. The wet resin was dried at 105° C. for 13hours in a tray drier. As a result, the dried resin (PPS) was recoveredat 1922 g (yield: 88%), and exhibited a melt viscosity of 194 Pa·s and abulk density of 0.37 g/cm³.

The temperature profile data and the bulk density data of the productare shown in Tables 1 and 2 appearing hereinafter together with those ofExamples and Comparative Examples described below;

Example 2

Polymerization, cooling and washing-drying were performed in the samemanner as in Example 1 except for changing the cooling temperatureprofile as shown in Table 1 by changing the conditions for water supplyto the condenser and air supply to the outer wall of the polymerizationvessel after the polymerization and cutting-off of the side-wall heaterat a temperature inside the vessel of 260° C. As a result, particulatePPS exhibiting a melt viscosity of 226 Pa·s and a bulk density of 0.37g/cm³ was obtained at a yield of 87%. The time period from the start ofthe cooling to 150° C. was 50 minutes.

Comparative Example 1

Polymerization, cooling and washing-drying were performed in the samemanner as in Example 1 except for changing the cooling temperatureprofile as shown in Table 2 by changing the conditions for water supplyto the condenser and air supply to the outer wall of the polymerizationvessel after the polymerization and cutting-off of the side-wall heaterat a temperature inside the vessel of 260° C. More specifically, aftercutting off the power supply to the heater, the system was cooled bystanding without water supply to the condenser or air supply to theouter wall of the polymerization. At a point of 77 minutes after thestart of the cooling by standing, a maximum system-viscosity temperatureof 234.3° C. was confirmed, and at 3.6 minutes thereafter, thetemperature reached 233.3° C. At this point, air supply to the outerwall of the polymerization vessel was started to accelerate the cooling.The time period from the start of the cooling to 150° C. was 150minutes.

As a result, particulate PPS exhibiting a melt viscosity of 150 Pa·s anda bulk density of 0.36 g/cm³ was obtained at a yield of 90%.

The bulk density of the product PAS particles was similar to those ofExamples 1 and 2, and therefore it is understood that gradual coolingover the entire course of cooling did not result in further improvementin particle properties of the product PAS.

Comparative Example 2

Polymerization, cooling and washing-drying were performed in the samemanner as in Example 1 except for changing the cooling temperatureprofile as shown in Table 2 by changing the conditions for water supplyto the condenser and air supply to the outer wall of the polymerizationvessel after the polymerization and cutting-off of the side-wall heaterat a temperature inside the vessel of 260° C. Cutting off of watersupply to the condenser for achieving a lower cooling speed in proximityto the maximum system-viscosity temperature (performed in the precedingExample) was not performed. As a result, particulate PPS exhibiting amelt viscosity of 145 Pa·s and a bulk density of 0.28 g/cm³ was obtainedat a yield of 90%. The time period from the start of the cooling to 150°C. was 59 minutes.

Thus, in spite of the fact that a uniform cooling speed of 1.7° C./min.was adopted over a temperature range of about 236-226° C. including themaximum system-viscosity temperature and a longer cooling time from thestart of cooling to 150° C. was used than in Example 1 and 2, the bulkdensity of the product PAS particles was substantially lowered to 0.28g/cm³ because the average cooling speed of 1.7° C./min. in thetemperature range of maximum system-viscosity temperature ±1° C. (and±2° C.) was excessively large.

Comparative Example 3

Polymerization, cooling and washing-drying were performed in the samemanner as in Example 1 except for changing the cooling temperatureprofile as shown in Table 2 by changing the conditions for water supplyto the condenser and air supply to the outer wall of the polymerizationvessel after the polymerization and cutting-off of the side-wall heaterat a temperature inside the vessel of 260° C. Cutting-off of watersupply to the condenser for achieving a lower cooling speed in proximityto the maximum system-viscosity temperature was not performed. As aresult, particulate PPS exhibiting a melt viscosity of 145 Pa·s and abulk density of 0.24 g/cm³ was obtained at a yield of 90%. The timeperiod from the start of the cooling to 150° C. was 29 minutes.

The product PAS particles exhibited a further lowered bulk density of0.24 g/cm³ presumably because the cooling speed in proximity to themaximum system-viscosity temperature was further higher than inComparative Example 2, so that the particles were understood to havelost particle properties suitable for transportation, storage, etc.

The outlines of cooling and the product bulk densities in the aboveExamples and Comparative Examples are inclusively shown in the followingTables 1 and 2. TABLE 1 Temperature profile in the cooling stage andproduct bulk density. (Examples) Example 1 Example 2 Cooling CoolingTemp. difference Time Temp. Speed Time Temp. Speed from MSVT* (° C.)(min.) (° C.) (° C./min.) (min.) (° C.) (° C./min.) (Cooling start) 0260 5.1 0 260 2.0 +5 5.0 234.7 4.0 11.8 236.1 2.2 +3 5.5 232.7 2.5 10.9234.1 2.0 +2 5.9 231.7 1.6 10.4 233.1 0.6 +1 6.5 230.7 ↑ 12 232.1 ↑   07.5 229.7 0.7 14 231.1 0.4 −1 9.5 228.7 ↓ 16.5 230.1 ↓ −2 10.5 227.7 1.017.7 229.1 0.8 −3 10.9 226.7 2.5 18.1 228.1 2.5 −5 11.5 224.7 3.3 18.9226.1 2.5 (Cooling end) 31 150 2.5 50 150 2.4 Bulk density 0.37 0.37(g/cm³)*MSVT = maximum system-viscosity temperature

TABLE 2 Temperature profile in the cooling stage and Product bulkdensity. (Comparative Examples) Temp. Comparative Example 1 ComparativeExample 2 Comparative Example 3 difference Cooling Cooling Cooling fromMSVT* Time Temp. Speed Time Temp. Speed Time Temp. Speed (° C.) (min.)(° C.) (° C./min.) (min.) (° C.) (° C./min.) (min.) (° C.) (° C./min.)(Cooling start) 0 260 0.3 0 260 2.1 0 260 11 +5 62.5 239.3 0.3 11.1236.2 1.8 3.0 227.5 10 +3 68.5 237.3 0.3 12.2 234.2 1.7 3.2 225.5 10 +271.4 236.3 0.4 12.8 233.2 1.7 3.3 224.5 10 +1 74.2 235.3 ↑ 13.4 232.2 ↑3.4 223.5 ↑   0 77 234.3 0.3 14 231.2 1.7 3.5 222.5 10 −1 80.6 233.3 ↓14.6 230.2 ↓ 3.6 221.5 ↓ −2 83.5 232.3 0.3 15.2 229.2 1.7 3.8 220.5 5.0−3 86.5 231.3 0.3 15.8 228.2 1.7 4.1 219.5 3.3 −5 90.5 229.3 0.5 17.0226.2 1.7 4.8 217.5 2.9 (Cooling end) 150 150 1.3 59 150 1.8 29 150 2.8Bulk density 0.36 0.28 0.24 (g/cm³)*MSVT = maximum system-viscosity temperature

INDUSTRIAL APPLICAPILITY

As described above, according to the present invention, there isprovided a process for producing through a relatively shortpolymerization cycle time such PAS particles having a high and stablebulk density as to exhibit good processability in transportation andstorage, and excellent transportability in a hopper or screw of anextruder or a molding machine.

1. A process for producing polyarylene sulfide, comprising: reacting anaromatic dihalide compound and an alkaline metal compound in a polarorganic solvent for polymerization under heating, and cooling a systemincluding the reaction mixture to recover particulate polyarylenesulfide, wherein the system after the reaction is gradually cooled at anaverage cooling speed of 0.2 to 1.0° C./min. selectively in atemperature range of maximum system-viscosity temperature ±1° C.
 2. Aprocess according to claim 1, wherein in the reaction under heating, aphase separation agent is added to a reaction system at a desired timefrom a start to an end of the reaction so as to form a liquid-liquidphase separation state including a thick phase and a dilute phase ofproduct polymer, and then the cooling is started.
 3. A process accordingto claim 2, wherein the phase separation agent is water.
 4. A processaccording to claim 3, wherein the alkaline metal compound is an alkalinemetal sulfide and the phase separation agent is water; the reactionunder heating includes a preceding step of reaction at a temperature ina range of 180° C. to 235° C. in the presence of 0.5 to 2.4 mols ofwater per mol of the charged alkaline metal sulfide to form a prepolymerat a conversion of 50 to 98 mol % of the aromatic dihalide compound, anda subsequent step of adding water so as to provide an amount of waterexceeding 2.5 mols and at most 7.0 mols per mol of the charged alkalinemetal sulfide in the reaction system and heating the system to atemperature of 245 to 290° C. to continue the reaction; and after thereaction, the cooling is started.
 5. A process according to claim 1,wherein the reaction and the cooling are performed in a reaction vesselequipped at its top with a reflux condenser as a principal cooling meansfor the cooling.
 6. A process according to claim 5, wherein during thecooling, at least a portion of non-condensable gaseous component isremoved from a top gaseous phase in the reflux condenser to enhance acooling capacity of the reflux condenser.
 7. A process according toclaim 1, wherein the system is cooled at a cooling speed exceeding 1.0°C./min. outside a temperature range of maximum system-viscositytemperature ±3° C.
 8. A process according to claim 7, wherein the systemis cooled at a cooling speed of at least 2.0° C./min. outside thetemperature range of maximum system-viscosity temperature ±3° C.
 9. Aprocess according to claim 1, wherein the system is cooled at a coolingspeed exceeding 1.0° C./min. outside a temperature range of maximumsystem-viscosity temperature ±2° C.
 10. A process according to claim 9,wherein the system is cooled at a cooling speed of at least 2.0° C./min.outside the temperature range of maximum system-viscosity temperature±2° C.
 11. A process according to claim 1, wherein the system is cooledat an average cooling speed of 0.2 to 1.0° C. in the temperature rangeof maximum system-viscosity temperature ±2° C.
 12. A process accordingto claim 2, wherein the reaction and the cooling are performed in areaction vessel equipped at its top with a reflux condenser as aprincipal cooling means for the cooling.
 13. A process according toclaim 3, wherein the reaction and the cooling are performed in areaction vessel equipped at its top with a reflux condenser as aprincipal cooling means for the cooling.
 14. A process according toclaim 4, wherein the reaction and the cooling are performed in areaction vessel equipped at its top with a reflux condenser as aprincipal cooling means for the cooling.
 15. A process according toclaim 2, wherein the system is cooled at a cooling speed exceeding 1.0°C./min. outside a temperature range of maximum system-viscositytemperature ±3° C.
 16. A process according to claim 3, wherein thesystem is cooled at a cooling speed exceeding 1.0° C./min. outside atemperature range of maximum system-viscosity temperature ±3° C.
 17. Aprocess according to claim 4, wherein the system is cooled at a coolingspeed exceeding 1.0° C./min. outside a temperature range of maximumsystem-viscosity temperature ±3° C.
 18. A process according to claim 5,wherein the system is cooled at a cooling speed exceeding 1.0° C./min.outside a temperature range of maximum system-viscosity temperature ±3°C.
 19. A process according to claim 6, wherein the system is cooled at acooling speed exceeding 1.0° C./min. outside a temperature range ofmaximum system-viscosity temperature ±3° C.
 20. A process according toclaim 2, wherein the system is cooled at a cooling speed exceeding 1.0°C./min. outside a temperature range of maximum system-viscositytemperature ±2° C.
 21. A process according to claim 3, wherein thesystem is cooled at a cooling speed exceeding 1.0° C./min. outside atemperature range of maximum system-viscosity temperature ±2° C.
 22. Aprocess according to claim 4, wherein the system is cooled at a coolingspeed exceeding 1.0° C./min. outside a temperature range of maximumsystem-viscosity temperature ±2° C.
 23. A process according to claim 5,wherein the system is cooled at a cooling speed exceeding 1.0° C./min.outside a temperature range of maximum system-viscosity temperature ±2°C.
 24. A process according to claim 6, wherein the system is cooled at acooling speed exceeding 1.0° C./min. outside a temperature range ofmaximum system-viscosity temperature ±2° C.
 25. A process according toclaim 2, wherein the system is cooled at an average cooling speed of 0.2to 1.0° C. in the temperature range of maximum system-viscositytemperature ±2° C.
 26. A process according to claim 3, wherein thesystem is cooled at an average cooling speed of 0.2 to 1.0° C. in thetemperature range of maximum system-viscosity temperature ±2° C.
 27. Aprocess according to claim 4, wherein the system is cooled at an averagecooling speed of 0.2 to 1.0° C. in the temperature range of maximumsystem-viscosity temperature ±2° C.
 28. A process according to claim 5,wherein the system is cooled at an average cooling speed of 0.2 to 1.0°C. in the temperature range of maximum system-viscosity temperature ±2°C.
 29. A process according to claim 6, wherein the system is cooled atan average cooling speed of 0.2 to 1.0° C. in the temperature range ofmaximum system-viscosity temperature ±2° C.
 30. A process according toclaim 7, wherein the system is cooled at an average cooling speed of 0.2to 1.0° C. in the temperature range of maximum system-viscositytemperature ±2° C.
 31. A process according to claim 8, wherein thesystem is cooled at an average cooling speed of 0.2 to 1.0° C. in thetemperature range of maximum system-viscosity temperature ±2° C.
 32. Aprocess according to claim 9, wherein the system is cooled at an averagecooling speed of 0.2 to 1.0° C. in the temperature range of maximumsystem-viscosity temperature ±2° C.
 33. A process according to claim 10,wherein the system is cooled at an average cooling speed of 0.2 to 1.0°C. in the temperature range of maximum system-viscosity temperature ±2°C.